The present invention relates to a control system for an internal combustion engine that performs catalyst temperature rise acceleration control for accelerating a rise in temperature of a catalyst for exhaust gas purification, and more particularly to a control system for performing such a catalyst temperature rise acceleration control and a lean-burn control for making the air-fuel ratio leaner.
The catalyst disposed in the exhaust system of an internal combustion engine for purifying exhaust gases is inactive at low temperatures. Consequently, the catalyst does not purify the exhaust gases at low temperatures. Therefore, there have been known a method of making the air-fuel ratio leaner than the stoichiometric air-fuel ratio to reduce emission of HC immediately after starting of the engine and a method of retarding ignition timing to accelerate a temperature rise of the catalyst. There is also known a control system which detects a property (volatility) of the fuel being used and controls the degree of making the air-fuel ratio leaner or the retard amount of the ignition timing according to the detected property of the fuel (Japanese Patent Laid-open No. Hei 9-53492).
By controlling the degree of making the air-fuel ratio leaner according to the detected property of the fuel, it is possible to make air-fuel ratio leaner to the limit which is suitable for the property of the fuel being used, thus effectively reducing the emission of HC.
However, the conventional system needs a fuel property sensor disposed in a fuel pipe, a combustion pressure sensor disposed in cylinders, or a pressure sensor in a fuel tank. Accordingly, there has been a problem that the system becomes complicated in structure.
An object of the present invention is to provide a control system for an internal combustion engine, which performs a catalyst temperature rise acceleration control immediately after starting of the engine by increasing an intake air amount and retarding ignition timing, and also performs a lean-burn control for making the air-fuel ratio leaner in a manner suitable for the property of the fuel being used with a simpler structure, to thereby effectively increase the temperature of the catalyst early and reduce emission of HC.
To achieve the above object, according to a first aspect of the present invention, there is a control system for an internal combustion engine having an exhaust system provided with a catalyst. The control system includes an intake air amount control for controlling an intake air amount of the engine. An ignition timing control for controlling the ignition timing of the engine. A catalyst temperature rise accelerating device for increasing the intake air amount immediately after starting the engine and retarding the ignition timing to make a rotational speed of the engine coincide with a target rotational speed. A lean control device for controlling the air-fuel ratio of an air-fuel mixture supplied to the engine to a lean region with respect to the stoichiometric ratio immediately after starting of the engine. The lean control device reduces the degree of making the air-fuel ratio leaner when the retard amount of the ignition timing during the operation of the catalyst temperature rise accelerating means is less than a predetermined retard amount.
With this configuration, the intake air amount immediately after starting of the engine is increased and the ignition timing is retarded to make the rotational speed of the engine coincide with a target rotational speed by the catalyst temperature rise accelerating means. The air-fuel ratio of an air-fuel mixture supplied to the engine immediately after starting of the engine is also controlled to a lean region with respect the stoichiometric ratio by the lean control means. The degree of making the air-fuel ratio leaner by the lean control means is suppressed when the retard amount of the ignition timing during the operation of the catalyst temperature rise accelerating means is less than a predetermined retard amount. Consequently, the lean air-fuel ratio control suitable for the property of the fuel being used can be carried out without the need for a fuel property sensor, to thereby effectively realize an early temperature rise of the catalyst and reduction of HC emission.
Preferably, the lean control means sets the predetermined retard amount according to the temperature of the engine.
With this configuration, since the predetermined retard amount is set according to the temperature of the engine, a fuel of low volatility can accurately be determined irrespective of the temperature of the engine.
Preferably, the lean control means sets the degree of making the air-fuel ratio leaner, according to the temperature of the engine and the load on the engine.
Preferably, the lean control means has averaging means for averaging a load parameter value indicative of the load on the engine, and sets the degree of making the air-fuel ratio leaner, using an averaged value calculated by the averaging means when the load parameter value is greater than the averaged value by a predetermined value.
Preferably, the lean control means has combustion state parameter calculating means for calculating a combustion state parameter indicative of the combustion state of the engine, and the lean control means suppresses the degree of making the air-fuel ratio leaner when the combustion state parameter indicates deterioration of the combustion state.
According to a second aspect of the present invention, there is provided a control system for an internal combustion engine having an exhaust system provided with a catalyst. The control system includes an intake air amount control for controlling an intake air amount of the engine. An ignition timing control controls the ignition timing of the engine. A catalyst temperature rise accelerator increases the intake air amount immediately after starting of the engine and retards the ignition timing to make a rotational speed of the engine coincide with a target rotational speed. A lean control device controls the air-fuel ratio of an air-fuel mixture supplied to the engine to a lean region with respect to a stoichiometric ratio immediately after starting of the engine. The lean control means has a fuel property determining device for determining a property of the fuel being used according to the retard amount of the ignition timing during the operation of the catalyst temperature rise accelerating means, and controls the degree of making the air-fuel ratio leaner according to the property of the fuel determined by the fuel property determining means.
With this configuration, the intake air amount immediately after starting of the engine is increased and the ignition timing is retared to make the rotational speed of the engine coincide with a target rotational speed by the catalyst temperature rise accelerating means, and the air-fuel ratio of an air-fuel mixture supplied to the engine immediately after starting of the engine is controlled to a lean region with respect the stoichiometric ratio by the lean control means. The property of the fuel being used is determined according to the retard amount of the ignition timing during the operation of the catalyst temperature rise accelerating means, and controls the degree of making the air-fuel ratio leaner according to the determined property of the fuel. Consequently, the lean air-fuel ratio control suitable for the property of the fuel being used can be carried out with simpler structure, to thereby effectively realize an early temperature rise of the catalyst and reduction or HC emission.
Preferably, the fuel property determining means determines the property of the fuel within a predetermined determination period (TMKLSTJG) from the completion of starting of the engine.